Many types of doors and hardware are used in hard traffic, commercial, institutional, and industrial door openings in buildings. When trying to achieve a specific function and design for an opening, the factors of aesthetics, security, safety, and resistance to abuse must be considered. Often, when double doors are installed at a particular location, a necessary piece of hardware is a center mullion. Depending on the design and function of the opening, a mullion may be permanently fixed in place to secure the doors, or the mullion can be engineered so that it is removable, for example with a key. Unfortunately, some mullions, especially electric mullions, that use electric strikes to secure an opening, are difficult to remove and reinstall. A second issue concerns the mullion sill block. A removable mullion that is locked in place to a header block at the top of the mullion, has a sill block at the bottom. It is fixed either to the floor, or the top of the threshold, and is concealed as it projects upward inside the bottom of the mullion tube. When the mullion is removed, the block is exposed and becomes a fixed projection that is a trip hazard in the opening. In this mode the block is easily dislodged or damaged when large, heavy objects have to be moved through the opening. It then has to be reattached or replaced in order to reinstall the mullion and lock the doors. The doors cannot be secured without having the mullion in place.